Rotary steerable system with optimized piston extension

ABSTRACT

A rotary steerable system including a steering section having at least one piston configured to extend a stroke length radially outward from a default position when activated. A ratio of the stroke length to a steering section diameter is greater than about 0.06. The steering section includes two piston sets. A ratio of a length of the piston to a diameter of the piston is between 1 and 1.4.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of, and priority to, U.S.Provisional Patent Application No. 63/207,487, filed on Mar. 2, 2021,which is incorporated herein by reference.

BACKGROUND

In the process of drilling and producing oil and gas wells, rotarysteerable systems are used to control and adjust the direction in whicha well is drilled. Conventional rotary steerable systems are well over150 inches in length and include three or more sets of extendingpistons. These large systems require frequent maintenance. Theconventional rotary steerable systems' long length presents challengesin the maintenance, including transporting the system from a drillinglocation to a shop.

BRIEF DESCRIPTION OF THE DRAWING VIEWS

FIG. 1 is a side view of a rotary steerable system of the presentinvention.

FIG. 2 is a sectional view of the rotary steerable system.

FIG. 3 is a sectional view of a control sleeve and a steering section ofthe rotary steerable system.

FIG. 4 is a partially exploded view of a control insert configured tofit within the control sleeve.

FIG. 5 is a partial sectional view of an upper control unit of thecontrol insert within the control sleeve.

FIG. 6 is an exploded view of a lower control unit of the controlinsert.

FIG. 7 is a sectional view of the lower control unit of the controlinsert.

FIG. 8 is a sectional view of the steering section.

FIG. 9 is a sectional view of the steering section taken along aperpendicular plane as compared to FIG. 8.

FIG. 10 is a sectional view of a lower portion of the control sectionand the steering section.

FIG. 11 is a top view of a valve stator of the rotary steerable system.

FIG. 12 is a sectional view of the valve stator of the rotary steerablesystem taken along line 12-12 in FIG. 11.

FIG. 13 is bottom view of the valve stator of the rotary steerablesystem.

FIG. 14 is a top view of an alternate embodiment of the valve stator ofthe rotary steerable system.

FIG. 15 is a sectional view of the alternate embodiment of the valvestator of the rotary steerable system taken along line 15-15 in FIG. 14.

FIG. 16 is bottom view of the alternate embodiment of the valve statorof the rotary steerable system.

FIG. 17 is a top view of a valve rotor of the rotary steerable system.

FIG. 18 is a sectional view of the valve rotor of the rotary steerablesystem taken along line 18-18 in FIG. 17.

FIG. 19 is bottom view of the valve rotor of the rotary steerablesystem.

FIG. 20 is a top view of the valve assembly including the valve rotorand the valve stator, with the valve rotor in a first position.

FIG. 21 is a sectional view of the valve assembly with the valve rotorin the first position taken along line 21-21 in FIG. 20.

FIG. 22 is a top view of the valve assembly with the valve rotor in asecond position.

FIG. 23 is a schematic view of the valve assembly with the valve rotorin a sequence of positions as it rotates relative to the valve stator.

FIG. 24 is a side view of the steering section in a default position.

FIG. 25 is a sectional view of the steering section in the defaultposition, taken along line 25-25 in FIG. 24.

FIG. 26 is a side view of the steering section in a first extendedposition.

FIG. 27 is a sectional view of the steering section in the firstextended position, taken along line 27-27 in FIG. 26.

FIG. 28 is a side view of the steering section in a neutral position.

FIG. 29 is a sectional view of the steering section in the neutralposition, taken along line 29-29 in FIG. 28.

FIG. 30 is a side view of the steering section in a second extendedposition.

FIG. 31 is a sectional view of the steering section in the secondextended position, taken along line 31-31 in FIG. 30.

FIG. 32 is a side view of an alternate embodiment of the steeringsection.

FIG. 33 is a sectional view of the alternate embodiment of the steeringsection.

FIG. 34 is a sectional view of the alternate embodiment of the steeringsection taken along line 34-34 in FIG. 32.

FIG. 35 is a sectional view of the alternate embodiment of the steeringsection taken along line 35-35 in FIG. 32.

FIG. 36 is a side view of the rotary steerable system connected betweena flex shaft and a drill bit.

FIG. 37 is another side view of the rotary steerable system connectedbetween the flex shaft and the drill bit.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

Disclosed herein is a rotary steerable system including a steeringsection. The steering section includes at least one piston. In someembodiments, the steering section includes only two pistons in eachtransverse cross-sectional plane. A center point of a first piston isseparated from a center point of a second piston by an angle greaterthan 120 degrees.

The rotary steerable system also includes a valve assembly configured todirect a portion of a drilling fluid flowing through the rotarysteerable system into a distribution flow passage, thereby activatingone of the pistons and causing the piston to extend in a radiallyoutward direction. A ratio of the diameter of each distribution flowpassage to the steering section diameter is at least 0.07. Thedistribution flow passages are contained within a central area of thesteering section. A ratio of the diameter of the central area to thesteering section diameter is 0.5 or less. An activation duration of eachset of pistons is about 180 degrees of rotation of a valve rotor. Aratio of the stroke length of each piston to the diameter of thesteering section is greater than 0.06. As used herein, “diameter of thesteering section” and “steering section diameter” both mean the minimumouter diameter of any portion of the assembled steering section (i.e.,the outer diameter of the smallest portion of the assembled steeringsection). For example, in some embodiments, the steering sectiondiameter may be the outer diameter of steering housing 22.

In some embodiments, the rotary steerable system also includes a controlsection. A combined length of the control section and the steeringsection is below 150 inches, preferably below 80 inches.

FIGS. 1-37 illustrate embodiments of the rotary steerable systemdisclosed herein, with many other embodiments within the scope of theclaims being readily apparent to skilled artisans after reviewing thisdisclosure.

With reference to FIGS. 1-3, rotary steerable system 10 includes controlsection 12 and steering section 14, each having a generally cylindricalshape. Control section 12 includes electronic components, sensors, andactuators for determining a drilling direction or tool face required andfor orienting the steering section.

Control section 12 includes control sleeve 16 and control insert 18disposed within inner bore 20 of control sleeve 16. Control insert 18 isconfigured for rotation relative to control sleeve 12. In oneembodiment, control insert 18 is configured to remain stationary withrespect to a surrounding subterranean formation, such that controlsleeve 16 rotates around control insert 18. In other words, controlinsert 18 may be configured to remain geo-stationary. A lower end ofcontrol sleeve 16 is secured to an upper end of steering housing 22 ofsteering section 14. In this way, control sleeve 16 is rotationallysecured to steering housing 22. As used herein, “rotationally secured”means secured together such that two components rotate together (i.e.,there is no relative rotation between two components under normaloperating conditions).

A lower end of control insert 18 includes a valve rotor 24, whichcooperates with valve stator 26 secured to steering housing 22. Valverotor 24 rotates relative to valve stator 26 as control insert 18rotates relative to control sleeve 16 and steering housing 22.

Referring now to FIGS. 2 and 4-6, control insert 18 may include uppercontrol unit 28, electronics unit 30, and lower control unit 32. Controlinsert 18 may also include guide 34 secured to upper control unit 28 andguide 36 secured to lower control unit 32. Guide 34 and 36 may berotationally secured to control sleeve 16, while upper and lower controlunits 28 and 32 rotate within guides 34 and 36, respectively. Controlinsert 18 may further include upper impeller 38 rotationally secured toupper control unit 28 and lower impeller 40 rotationally secured tolower control unit 32. Upper and lower impellers 38 and 40 may be sizedand configured such that the outer ends of impellers 38 and 40 are inclose proximity a surface of inner bore 20 of control sleeve 16. Guides34 and 36 and impellers 38 and 40 may stabilize a position of controlinsert 18 within inner bore 20 of control sleeve 16 while control insert18 therein.

Referring again to FIG. 2, upper control unit 28 may include a magneticbrake 41, which functions as an actuator to apply rotational torque in adirection that is opposite to a rotational direction of control sleeve16 and steering housing 22. In this way, the magnetic brake assemblyadjusts the rotation rate of control insert 18 relative to controlsleeve 16. As a drilling fluid flows through inner bore 20 of controlsleeve 16, the drilling fluid flows through spaces in impeller 38,thereby applying a rotational force on impeller 38 and upper controlunit 28. In one embodiment, upper control unit 28 also includes a powergeneration mechanism. The magnetic brake assembly may be the onlyactuator in rotary steerable system 10.

With reference to FIGS. 4 and 5, upper control unit 28 may also includeupper filter 44. In one embodiment, upper filter 44 may be formed ofrings with shoulders such that the stacking of the rings creates smallinterstices that function to filter. As drilling fluid flow throughinner bore 20 of control sleeve 16, a small amount of drilling fluid mayflow through upper filter 44 and through intermediate spaces 43 a, 43 b,43 c, and 43 d surrounding antenna 42 and magnetic brake 41. Upperfilter 44 removes larger particles from the drilling fluid to allow asmall amount of clean fluid to flow in the intermediate spaces 43 a-43d. Allowing only clean fluid to flow in intermediate spaces 43 a-43 dprevents the two parts of upper control unit 28 from seizing up and/orfrom creating additional drag between the two parts of upper controlunit 28. The majority of the drilling fluid flows around the exteriorsurface of filter 44 and through the spaces in impeller 38.

Electronics unit 30 may include sensors. For example, electronics unit30 may include a magnetometer for sensing a north-south direction, anaccelerometer for sensing inclination, and a gyrometer for sensingrotation of the control unit relative to a surrounding subterraneanformation. Control insert 18 may be configured to adjust the magneticbrake assembly in the upper control unit 28 based on measurements takenby the sensors in electronics unit 30. In some embodiments, the rotarysteerable system 10 includes no batteries and only a small amount ofmemory (e.g., flash memory only). In these embodiments, the electronicsunit 30 may include antenna 42 for transmitting measurement data andother data to a measurement-while-drilling (“MWD”) unit secured abovethe rotary steerable system 10, and the MWD unit may store the receiveddata in a memory. Antenna 42 of the electronics unit 30 may be formed ofan electromagnetic antenna.

With reference to FIGS. 6 and 7, lower control unit 32 may includehousing 45 with flow passages 46. Flow passages 46 are configured toallow a drilling fluid in an annular space between control sleeve 16 andhousing 45 to flow into inner space 48 within housing 45. Lower controlunit 32 may also include lower filter 49 configured to surround andcover flow passages 46 in order to filter drilling fluid as it flowsthrough flow passages 46 and enters inner space 48. In one embodiment,lower filter 49 may be formed of rings with shoulders such that thestacking of the rings creates small interstices that function to filter.Lower control unit 32 may further include spring 50 disposed withininner space 48 and configured to bias valve rotor 24 in a directiontoward the valve stator 26 and steering section 14. For example, anupper end of spring 50 may engage transverse surface 52 of housing 45,while lower end of spring 50 engages an upper end of spacer 54 to applya downward force on the valve rotor 24, which is secured to a lower endof spacer 54. As a drilling fluid flows through the annular spacebetween control sleeve 16 and housing 45, a portion of the drillingfluid may flow through flow passages 46, into inner space 48, andthrough a rotor port 56 of valve rotor 24. The remainder of the drillingfluid flowing through the annular space may flow through spaces inimpeller 40 outside of housing 45.

With reference now to FIGS. 8 and 9, steering section 14 includesparallel main flow passages and distribution flow passages. Steeringhousing 22 includes two main flow passages 66 extending from upper innerbore 68 to lower inner bore 70. Steering housing 22 also includes twodistribution flow passages 72, each extending from a stator port 73 ofvalve stator 26 to one or more feed channels 74. Steering section 14also includes two piston assemblies 76, each at least partially securedwithin a receptacle 78 in an outer surface of steering housing 22. Eachpiston assembly 76 includes one or more pistons 80 each disposed withina piston sleeve 85, all disposed within piston clamp 81, which isconfigured to be secured within piston receptacle 82 in steering housing22. Pistons 80 are configured to slide in a radial direction withinpiston receptacles 82. Each feed channel 74 extends from a distributionflow passage 72 to a piston receptacle 82. Steering section 14 of rotarysteerable system 10 may include not more than two pistons in eachtransverse cross-sectional plane, with the center points of the pistonsseparated by an angle greater than 120 degrees. Steering section 14 mayinclude not more than two sets of pistons.

Steering section 14 may further include spacers 84, each at leastpartially disposed within spacer receptacles 86 in an outer surface ofsteering housing 22. In one embodiment, spacers 84 are secured tosteering housing 22 using bolts or screws. As used herein, “piston”means any structure configured to extend, when activated, in a radialdirection from a tool to which it is secured or in which it isincorporated. For example, “piston” includes a pad, a wedge arrangement,and a cam arrangement.

Referring to FIG. 10, as a drilling fluid flows through the annularspace between control sleeve 16 and control insert 18, a portion of thedrilling fluid may flow through flow passages 46 and into inner space 48of housing 45. The drilling fluid within inner space 48 may flow throughrotor port 56 of valve rotor 24 and through a stator port 73 of valvestator 26 that is aligned with rotor port 56. As valve rotor 24 rotatesrelative to valve stator 26, rotor port 56 aligns with each of thestator ports 73 in sequence over time. Accordingly, the drilling fluidflowing through rotor port 56 will flow through each of the stator ports73 in sequence over time. Drilling fluid that flows through one of thestator ports 73 flows through the connecting distribution flow passage72, through each of the connected feed channels 74, and into connectedpiston receptacles 82 in order to apply a force and displace piston 80in a radial outward direction. In some embodiments, and in order toprovide an exhaust path for when the piston retracts from an openposition, the drilling fluid can flow through leak channels 90 betweenpistons 80 and piston receptacles 82, or in another embodiment, it mayleak between the piston and the guide sleeve, through diametral spacebetween the two or through a channel formed in the sleeve or in thepiston that connect piston receptacles 82 to the wellbore. In anotherembodiment, the leak channels may be located through the piston body toconnect piston receptacles 82 to the wellbore. In another embodiment,the leak channel may be located between the guide sleeve and thesteering body.

FIGS. 11-13 illustrate one embodiment of valve stator 26, which includestwo stator ports 73 positioned on opposite sides of valve stator 26. Inother words, the central point of the outer boundary of one stator port73 is 180 degrees from the central point of the outer boundary of thesecond stator port 73. In this embodiment, the shape of each stator port73 varies across the thickness of valve stator 26. For example, eachstator port 73 may be defined by a wedge-shaped opening 92 on first side94 of valve stator 26 and defined by a circular opening 96 on secondside 98 of valve stator 26. First side 94 is configured to engage valverotor 24, and second side 96 is configured to engage distribution flowpassages 72. The sides of the wedge-shaped opening 92 may be formed ofstraight lines, which align with side boundaries of rotor port 56 toprovide sharper actuations of pistons. While the circular openings 96are configured to align with the distribution flow passages 72. Thetransition of the shape of stator ports 73 across the thickness of valvestator 26 reduces the length of transition flow lines needed between thevalve assembly and the pistons 80. In other embodiments, each statorport 73 may be defined by wedge-shaped opening 92 on first side 94 ofvalve stator 26 and defined by a polygon-shaped opening on second side98 of valve stator 26. In still other embodiments, stator ports 73 mayhave the same shape across the thickness of valve stator 26.

FIGS. 14-16 illustrate an alternate embodiment of valve stator 26 a. Inthis embodiment, each stator port 73 a is defined by a wedge-shapedopening 92 a on first side 94 a of valve stator 26 a. Each stator port73 a is defined by a polygon-shaped opening 99 on second side 98 a ofvalve stator 26 a.

FIGS. 17-19 illustrate one embodiment of valve rotor 24, which includesonly one rotor port 56. In this embodiment, the shape of rotor port 56varies across the thickness of valve rotor 24. For example, rotor port56 may be defined by inner boundary 102, outer boundary 106, and sideboundaries 108 and 110 on first side 104 of valve rotor 24. Sideboundaries 108 and 110 interconnect inner and outer boundaries 102 and106 on first side 104. A center point of first side 104 is positionedbetween inner boundary 102 and outer boundary 106. In other words, rotorport 56 includes the center point of first side 104. Inner boundary 102of rotor port 56 remains constant throughout the thickness of valverotor 24. On second side 112 of valve rotor 24, rotor port 56 may bedefined by outer boundary 106, inner boundary 114, and side boundaries116 and 118. Side boundaries 116 and 118 interconnect inner and outerboundaries 102 and 106 on second side 112. Inner boundary 114 ispositioned between outer boundary 106 and a center point of second side112. In other words, the center point of second side 112 is not includedwithin rotor port 56. Valve rotor 24 may include sloped surface 120 inthe transitions between inner boundaries 102 and 114, side boundaries108 and 116, and side boundaries 110 and 118, respectively.

Side boundaries 116 and 118 of first side 104 of rotor port 56 may havethe same shape as the side boundaries of wedge-shaped openings 92 ofstator ports 73. For example, each of the side boundaries 116 and 118and each of the side boundaries of wedge-shaped openings 92 may beformed of a straight line extending in a radial direction.

Referring now to FIGS. 20-22, valve assembly 124 may include valve rotor24 and valve stator 26, with valve rotor 24 rotating relative to valvestator 26. In this embodiment, outer boundary 106 of rotor port 56aligns with the outer boundary of wedge-shaped openings 92 of statorports 73, and inner boundary 114 of rotor port 56 aligns with the innerboundary of wedge-shaped openings 92 of stator ports 73. In a firstposition shown in FIGS. 20 and 21, rotor port 56 is aligned with all ofthe wedge-shaped opening 92 of a single stator port 73. In this firstposition, a first stator port 73 a is “open” and a second stator port 73b (not shown in this view) is “closed.” As valve rotor 24 rotates, theside boundaries 116 and 118 of rotor port 56 cross over the sideboundaries of wedge-shaped openings 92 of stator ports 73, therebyalternately opening and closing stator ports 73 a and 73 b. The angularseparation of side boundary 116 from side boundary 118 and the angularseparation of the two side boundaries of each wedge-shaped opening 92together define the duration for which each stator port 73 is open(i.e., activation duration of each stator port 73). These angularseparations also define whether both stator ports 73 are partially openat a single point in time, and if so, the duration for which both statorports 73 are simultaneously partially open. In certain embodiments, theopening angle of the rotor port 56 (i.e., the angular distance betweenside boundaries 116 and 118 within rotor port 56) is at least 110degrees. As used herein, “opening angle” is the rotational distancebetween two radial boundaries within an opening. In some embodiments,the side boundaries of the two wedge-shaped openings 92 are separated byat least 110 degrees or between 110 degrees and 170 degrees, or anysubrange therein. In certain embodiments, the side boundaries of the twowedge-shaped openings 92 are separated by at least 125 degrees. Infurther embodiments, the side boundaries of the two wedge-shapedopenings 92 are separated by an angle between 140 degrees and 170degrees. In a second position shown in FIG. 22, rotor port 56 is alignedwith a portion of stator port 73 a and a portion of stator port 73 b.

FIG. 23 illustrates valve assembly 124 with valve rotor 24 in varioussequential positions relative to valve stator 26 over time. In thisembodiment, valve rotor 24 rotates in a counter-clockwise direction. Inother embodiments, valve rotor 24 rotates in a clockwise direction. Instill other embodiments, valve rotor 24 is maintained in a geostationaryposition while valve stator 26 rotates with steering unit 14 and controlsleeve 16 in a clockwise direction. FIG. 23(a) illustrates the firstposition shown in FIGS. 20 and 21, in which rotor port 56 is alignedwith first stator port 73 a such that first stator port 73 a is fullyopen and second stator port 73 b is closed. First stator port 73 aremains fully open through the time when side boundary 116 of rotor port56 aligns with a side boundary of the wedge-shaped opening of firststator port 73 a, as shown in FIG. 23(b).

As shown in FIG. 23(c), further rotation of valve rotor 24 causes sideboundary 116 of rotor port 56 to move across first stator port 73 athereby reducing the open cross-sectional area of first stator port 73 aand reducing the fluid flow rate through first stator port 73 a. Thefirst stator port 73 a is partially open and the second stator port 73 bis closed through the time when side boundary 118 of rotor port 56aligns with a first side boundary of the wedge-shaped opening of secondstator port 73 b, as shown in FIG. 23(c). Further rotation of valverotor 24 causes side boundary 118 of rotor port 56 to move past thefirst side boundary of second stator port 73 b, thereby placing bothfirst and second stator ports 73 a and 73 b in partially open positions,as shown in FIG. 23(d). In this embodiment, the valve assembly isconfigured to have first and second stator ports 73 a and 73 b partiallyopen simultaneously as shown in FIG. 23(d). The valve assembly remainsin this simultaneous partially open position until side boundary 116aligns with a second side boundary of first stator port 73 a to placefirst stator port 73 a in the closed position, as shown in FIG. 23(e).As valve rotor 24 rotates further and side boundary 118 of rotor port 56moves across the second stator port 73 b, second stator port 73 b isfurther opened and the fluid flow rate through the second stator port 73b increases. During this time, first stator port 73 a is closed andsecond stator port 73 b is partially open.

As shown in FIG. 23(f), second stator port 73 b is placed in a fullyopen position when side boundary 118 of rotor port 56 aligns with asecond side boundary of second stator port 73 b. Second stator port 73 bremains in the fully open position through the time when side boundary116 of rotor port 56 aligns with the first side boundary of secondstator port 73 b as shown in FIG. 23(g).

As shown in FIG. 23(h), further rotation of valve rotor 24 causes sideboundary 116 of rotor port 56 to move across second stator port 73 b,thereby reducing the open cross-sectional area of second stator port 73b and reducing the fluid flow rate therethrough. The first stator port73 a is closed and the second stator port 73 b is partially open throughthe time when side boundary 118 of rotor port 56 aligns with the firstside boundary of first stator port 73 a, as shown in FIG. 23(h). Furtherrotation of valve rotor 24 causes side boundary 118 of rotor port 56 tomove past the first side boundary of first stator port 73 a to placeboth stator ports 73 a and 73 b in partially open positions, as shown inFIG. 23(i). The valve assembly remains in this simultaneous partiallyopen position until side boundary 116 of rotor port 56 aligns with thesecond side boundary of second stator port 73 b to place second statorport 73 b in the closed position, as shown in FIG. 23(j). As valve rotor24 continues to rotate and side boundary 118 of rotor port 50 movesacross the first stator port 73 a, first stator port 73 a is furtheropened and the fluid flow rate through the first stator port 73 aincreases. During this time, first stator port 73 a is partially openand second stator port 73 b is closed. As shown in FIG. 23(k), firststator port 73 a is placed in the fully open position when side boundary118 of rotor port 56 aligns with the second side boundary of firststator port 73 a. FIG. 23(l) again illustrates the valve assembly in thefirst position, in which first stator port 73 a is fully open and secondstator port 73 b is closed. Table 1 lists the positions of the statorports in each view of FIG. 23.

TABLE 1 Position of Position of FIG. First stator port 73a Second statorport 73b FIG. 23(a) Fully open Closed FIG. 23(b) Fully open Closed FIG.23(c) Partially open Closed FIG. 23(d) Partially open Partially openFIG. 23(e) Closed Partially open FIG. 23(f) Closed Fully open FIG. 23(g)Closed Fully open FIG. 23(h) Closed Partially open FIG. 23(i) Partiallyopen Partially open FIG. 23(j) Partially open Closed FIG. 23(k) Fullyopen Closed FIG. 23(l) Fully open Closed

The theoretical activation duration of each stator port 73 a, 73 b(i.e., the rotation of valve rotor 24 for which such stator port 73 a or73 b is fully or partially open) may be greater than 120 degrees,preferably greater than 150 degrees, and most preferably about 180degrees. The embodiment illustrated in FIG. 23 provides a theoreticalactivation duration of about 180 degrees. Second stator port 73 b ispartially or fully open from the time that side boundary 118 of rotorport 56 crosses the first side boundary of second stator port 73 b(immediately after the position illustrated in FIG. 23(c)) until thetime that side boundary 116 crosses the second side boundary of secondstator port 73 b (immediately before FIG. 23(j)).

FIGS. 24 and 25 illustrate steering section 14 in a default position inwhich pistons 80 are in retracted positions. This embodiment of rotarysteerable system 10 includes two pistons 80, with the center points ofthe two pistons 80 separated by about 180 degrees. Because steeringsection 14 includes only two pistons 80 in each transversecross-sectional plane, distribution flow passages 72 a and 72 b may bepositioned within a central area of steering housing 22. In someembodiments, main flow passages 66 may extend from the central areaoutward radially. Distribution flow passages 72 a, 72 b and main flowpassages 66 may be positioned between piston receptacles 82. Optionally,main flow passages 66 may also extend beyond the space between pistonreceptacles 82. The position of the distribution flow passages 72 a, 72b in the central area within the same transverse cross-sectional planeas pistons 80 eliminates the need for a spider to rearrange flow linesthrough a length of the steering unit (i.e., distribution flow passagesremain in the central area from the valve assembly 124 to the feedchannels 74 and pistons 80).

In certain embodiments, the central area may be defined by a circularpath that includes the center of the inner boundary of each pistonreceptacle 82 and is centered on the center of the steering unit 14. Inother embodiments, the central area may be defined by a central diametersurrounding the center of the steering unit 14. The central diameter maybe in the range of 1.5 inches to 3.0 inches, preferably about 1.75inches to about 2.5 inches, or any subrange therein. In certainembodiments, the central diameter may be about 1.75 inches in a steeringunit having a diameter less than or equal to 5.25 inches, about 2 inchesin a steering unit having a diameter less than or equal to 6.75 inches,and about 2.5 inches in a steering unit having a diameter less than orequal to 9 inches. A ratio of the central diameter to the steeringsection diameter may be 0.5 or less, 0.4 or less, preferably 0.33 orless, more preferably 0.3 or less.

In the embodiment illustrated in FIG. 25, steering section 14 includesaxis x and axis y intersecting at the central point of steering section14 as shown. The central area in which distribution flow passages 72 arepositioned is defined by distribution distance 90 between the centralpoint and a line D extending from an outer most point on one of thedistribution flow passages 72. Line M is defined by the inner boundaryof one of the main flow passages 66. Line M is spaced apart from thecentral point by main distance 92. Line P is defined by the innerboundary of one of the piston receptacles 82. Line P is spaced apartfrom the central point by piston distance 94. In this embodiment,distribution distance 90 is greater than main distance 92, and pistondistance 94 is greater than distribution distance 90. In other words, atleast a portion of each main flow passage 66 is closer to the centralpoint of the steering section than the outer boundary of thedistribution flow passages 72. Additionally, at least a portion of eachmain flow passage 66 is closer to the central point of the steeringsection than the inner boundary of the piston receptacle 82 and theposition of the piston in its retracted position.

The rotary steerable system disclosed herein includes distribution flowpassages 72 a, 72 b having larger diameters and main flow passages 66having larger diameters than in conventional rotary steerable systems.The larger diameters of these flow lines reduce the fluid flow speed,prevent a water hammer effect, reduce erosion, and reduce pressure dropin order to preserve energy. A ratio of a diameter of each distributionflow passage 72 a, 72 b to a diameter of steering section 14 may be atleast 0.07. In certain embodiments, a diameter of each distribution flowpassage 72 a, 72 b is about 0.35 inches in a steering section 14 havinga diameter of at least 5.25 inches, about 0.5 inches in a steeringsection 14 having a diameter of at least 6.75 inches, and about 0.67inches in a steering section 14 having a diameter of at least 9 inches.

With reference to FIGS. 10, 13, and 20-23, valve assembly 124 (shown inFIGS. 20-23) may be positioned at the upper end of the distribution flowpassages (shown in FIG. 10) such that circular openings 96 on the secondside 98 of stator ports 73 (shown in FIG. 13) align with distributionflow passages 72. Specifically, circular opening 96 of stator port 73 aaligns with distribution flow passage 72 a, and circular opening 96 ofstator port 73 b aligns with distribution flow passage 72 b. As valverotor 24 rotates relative to valve stator 26 (as shown in FIG. 23),stator ports 73 a and 73 b circulate through fully open, partially open,and closed positions, thereby directing fluid flowing through innerspace 48 within housing 45 of lower control unit 32 into firstdistribution flow passage 72 a, second distribution flow passage 72 b,or a combination thereof.

FIGS. 26 and 27 illustrate steering assembly 14 in a first extendedposition when first stator port 73 a is fully open (as shown in FIGS.23(a) and 23(b)). In this position, valve assembly 124 directs the fluidwithin inner space 48 of lower control unit 32 into first distributionflow passage 72 a. Specifically, the drilling fluid that has enteredinner space 48 of lower control unit 32 flows through rotor port 56 ofvalve rotor 24, through first stator port 73 a, through firstdistribution flow passage 72 a, through feed channels 74, and into firstpiston receptacles 82 a. The fluid flowing into first piston receptacles82 a applies a radial outward force on first pistons 80 a, therebycausing first pistons 80 a to move in a radially outward direction. Inthis first extended position, first pistons 80 a may engage a wall of awellbore being drilled through a subterranean formation in order toadjust the direction in which the wellbore is drilled further. Thedrilling fluid that flows through the spaces in impeller 40 flowsthrough main flow passages 66, thereby bypassing the piston assemblies76.

Referring again to FIG. 27, each piston 80 a and 80 b may have a lengthof L_(p) and a diameter of D. In some embodiments a ratio of eachpiston's length to the piston's width is between 1 and 1.4, preferablybetween 1.1 and 1.3, or any subrange therein. For example, each of thepistons may have a length of 2.09 inches and a diameter of 1.73 inches,resulting in a ratio of about 1.2. In another example, the pistons mayhave a length of 2.88 inches and a diameter of 2.43 inches, resulting ina ratio of about 1.2. In yet another example, the pistons may have alength of 3.78 inches and a diameter of 3.12 inches, resulting in aratio of about 1.2.

Additionally, each piston 80 a and 80 b extends a stroke length S fromits default position when activated. The pistons may have a ratio ofstroke length to piston diameter that is greater than 0.06, preferablygreater than 0.7, or about 0.08. For example, the stroke length of thepiston may be between 0.3 inches and 0.5 inches in an embodiment havinga steering section diameter of at least 5.25 inches. In another example,the stroke length of the piston may be between 0.4 inches and 0.6 inchesin an embodiment having a steering section diameter of at least 6.75inches. In yet another example, the stroke length of the piston may bebetween 0.6 inches and 0.8 inches in an embodiment having a steeringsection diameter of at least 9 inches

FIGS. 28 and 29 illustrate steering assembly 14 in a neutral positionwhen first and second stator ports 73 a, 73 b are both partially open(as shown in FIGS. 23(d) and 23(i)). In this position, valve assembly124 directs the fluid within inner space 48 of lower control unit 32into both first and second distribution flow passages 72 a, 72 b. As thefluid flow through first stator ports 73 a and ultimately into pistonreceptacles 82 a decreases, a force exerted by a wall of a wellbore onpistons 80 a may overcome the outward force of the fluid flow intopiston receptacles 82 a, which may force pistons 80 a to retract in aradially inward direction into piston receptacles 82 a. The excess fluidin receptacle 82 a is expelled through the exhaust port. Simultaneously,the drilling fluid flowing through second stator port 73 b flows throughsecond distribution flow passage 72 b, through feed channels 74, andinto piston receptacles 82 b. The fluid flowing into piston receptacles82 b begins to apply a radial outward force on second pistons 80 b,thereby causing second pistons 80 b to begin moving in a radiallyoutward direction.

FIGS. 30 and 31 illustrate steering assembly 14 in a second extendedposition when second stator port 73 b is fully open (as shown in FIGS.23(f) and 23(g)). In this position, valve assembly 124 directs all fluidwithin inner space 48 of lower control unit 32 into second distributionflow passage 72 b. As the fluid flow through second stator ports 73 band ultimately into piston receptacles 82 b increases, the fluid flowapplies a greater radial outward force on second pistons 80 b, therebycausing second pistons 80 b to fully extend in the radially outwarddirection. In this second extended position, second pistons 80 b mayengage the wall of the wellbore in order to adjust the drilling in anopposite direction. In all positions of the steering assembly 14, thedrilling fluid that flows through the spaces in impeller 40 flowsthrough main flow passages 66, thereby bypassing the piston assemblies76.

The theoretical activation duration of each piston 80 a, 80 b (i.e., therotation of valve rotor 24 for which each piston 80 a, 80 b is fully orpartially extended) is equivalent to the theoretical activation durationof each stator port 73 a, 73 b, which is discussed above. Rotarysteerable system 10 may be configured to provide a theoreticalactivation duration of each piston 80 a, 80 b that is greater than 120degrees, preferably greater than 150 degrees, and most preferably about180 degrees. The actual observed activation duration of each piston 80a, 80 b may be less than the theoretical activation duration because ofactuation timing delays. As used herein, “activation duration” means theangle of rotation of valve rotor 24 during which a specified componentis activated by or receives by fluid flow. The two-piston configurationof the rotary steerable system disclosed herein may provide a greateractivation duration of each piston as compared to conventional rotarysteerable systems including three-piston configurations due to fewertransitions in each rotation of the valve and due to larger angularseparation of the side boundaries of each stator port.

Steering section 14 may include any number of pistons within the pistonassemblies. In this embodiment illustrated in FIGS. 32-35, steeringsection 14 includes a first piston assembly 76 a including two pistons80 a and a second piston assembly 76 b including three pistons 80 b. Inthe illustrated embodiment pistons 80 a may be staggered along the axiallength of steering housing 22 relative to pistons 80 b, as shown in FIG.33. In other words, the steering section 14 includes only one piston ina transverse cross-sectional plane, such as plane A—A. In otherembodiments, the offset pistons are separated by a length that is equalto the steering section diameter. Alternatively, the steering section 14may include only a one piston.

Referring now to FIGS. 36 and 37, rotary steerable system 10 may besecured below flex shaft 152 and drill bit 154 in a bottom holeassembly.

The rotary steerable system of the present invention, which includes asteering section and a control section, is significantly shorter thanconventional rotary steerable systems. The combined length of thesteering section and the control section is less than 150 inches, lessthan 125 inches, less than 100 inches, less than 80 inches, less than 75inches, less than 70 inches, less than 65 inches, or any subrangetherein. In one embodiment, the rotary steerable system has a minimumdiameter of about 5.25 inches, and a combined length of about 63 inches.In another embodiment, the rotary steerable system has a minimumdiameter of about 6.75 inches, and a combined length of about 67 inches.In still another embodiment, the rotary steerable system has a minimumdiameter of about 9 inches, and a combined length of about 74 inches.

Alternatively, the rotary steerable system has a length to steeringsection diameter ratio of less than 16, less than 14, less than 11, lessthan 10, less than 9, or any subrange therein. As used herein, “lengthto steering section diameter ratio” means a ratio of the combined lengthof the steering section and control section to the minimum outerdiameter of the steering section or the control section (in inches). Forexample, but not by way of limitation, the rotary steerable system mayhave a diameter less than or equal to 5.25 inches, and a length tosteering section diameter ratio of less than 13, less than 12, or anysubrange therein. Alternatively, the rotary steerable system may have adiameter less than or equal to 6.75 inches, and a length to steeringsection diameter ratio of less than 11, less than 10, or any subrangetherein. In other embodiments, the rotary steerable system may have adiameter less than or equal to 9 inches, and a length to steeringsection diameter ratio of less than 9.

With reference again to FIGS. 36 and 37, flex shaft 152 may be securedabove rotary steerable system 10, and drill bit 154 may be secured belowrotary steerable system 10. The reduced length of the rotary steerablesystem 10 positions flex shaft 152 closer to drill bit 154 than inconventional rotary steerable systems, thereby enabling the rotarysteerable system to turn the drill bit path by a smaller radius. Forexample, the rotary steerable system disclosed herein may enable amaximum turn rate of 14 degrees per 100 feet. In another embodiment, therotary steerable system disclosed herein may enable a maximum turn rateof 18 degrees per 100 feet. In yet another embodiment, the rotarysteerable system disclosed herein may enable a maximum turn rate of 24degrees per 100 feet. In effect, the reduced length rotary steerablesystem 10 behaves as a hybrid push-the-bit/point-the-bit system ascontrol unit 12 and steering unit 14 are deflected (i.e., pushed) as oneand become pointed in the desired direction. The maximum turn ratevalues may be affected by environmental conditions, including conditionswithin a wellbore or conditions of a subterranean formation.

The reduced length of the rotary steerable system of the presentinvention is achieved due to several features. For example, lower filter49 and valve assembly including valve rotor 24 and valve stator 26 areincorporated into a single module, as shown in FIG. 10. In contrast,conventional rotary steerable systems include separate modules forfilters and valves. Additionally, the absence of a battery reduces thelength of control section 12. Another example is the use of smallermemory components, such as micro-electromechanical systems (“MEMS”), inthe control section 12. Conventional rotary steerable systems teach awayfrom smaller memory components in favor of larger memory componentscapable of storing data required for well surveys. Further, the rotarysteerable system disclosed herein includes only three sensors in controlsection 12, thereby reducing the length of the control section 12.Conventional rotary steerable systems include a greater number ofsensors, which require a greater length of the control section. Anotherexample is the transition of the shape of stator ports 73 across thethickness of valve stator 26, which reduces the length of transitionflow lines needed in steering housing 22 between the valve assembly andthe pistons 80. Furthermore, the central position of distribution flowreceptacles 72 within steering section 14 eliminates the requirement fora spider, which transposes the main flow and distribution flow linesbetween the valve and pistons in conventional rotary steerable systems.

The reduced length of the rotary steerable system disclosed hereinprovides the commercial advantage of requiring less material forconstruction, thereby reducing costs of manufacturing and maintenance.In some embodiments, the components of the rotary steerable systemdisclosed herein are more accessible from outside of the rotarysteerable system, which enables users to perform certain additionalmaintenance tasks in any location without the need for transporting therotary steerable system to a shop.

In other embodiments, the rotary steerable system of the presentinvention includes only a steering section without a control section. Inthis embodiment, the elements of the control section may be incorporatedinto the steering section, positioned in adjacent devices in the drillstring, eliminated, or any combination thereof.

As illustrated in FIGS. 2-9, the rotary steerable system disclosedherein, such as rotary steerable system 10, includes nine modules, witheach module comprising a unit that may be maintained, assembled,disassembled, or exchanged independently of the other modules. Themodules of the rotary steerable system disclosed herein are listed inTable 2 below.

TABLE 2 Modules of steering Steering housing 22 section 14 Pistons 80Piston clamps 81 Spacers 84 Screw sets for spacers 84 Modules of controlControl sleeve 16 section 12 Guides 34, 36 with bolts Electronics 30,lower control unit 32, and inner portions of upper control unit 28Housing of upper control unit 28

As used herein, “upper” and “lower” are to be interpreted broadly toinclude “proximal” and “distal” such that the structures may not bepositioned in a vertical arrangement. Additionally, the elementsdescribed as “upper” and “lower” may be reversed such that thestructures may be configured in the opposite vertical arrangement.

Except as otherwise described or illustrated, each of the components inthis device has a generally cylindrical shape and may be formed ofsteel, another metal, or any other durable material. Portions of therotary steerable system may be formed of a wear resistant material, suchas tungsten carbide or ceramic coated steel.

Each device described in this disclosure may include any combination ofthe described components, features, and/or functions of each of theindividual device embodiments. Each method described in this disclosuremay include any combination of the described steps in any order,including the absence of certain described steps and combinations ofsteps used in separate embodiments. Any range of numeric valuesdisclosed herein includes any subrange therein. “Plurality” means two ormore. “Above” and “below” shall each be construed to mean upstream anddownstream, such that the directional orientation of the device is notlimited to a vertical arrangement.

While preferred embodiments have been described, it is to be understoodthat the embodiments are illustrative only and that the scope of theinvention is to be defined solely by the appended claims when accorded afull range of equivalents, many variations and modifications naturallyoccurring to those skilled in the art from a review hereof.

We claim:
 1. A rotary steerable system, comprising a steering section, wherein the steering section includes at least one piston, wherein the piston is configured to extend a stroke length radially outward from a default position when activated, and wherein a ratio of the stroke length to a steering section diameter is greater than about 0.06, wherein the steering section diameter is a minimum diameter of the steering section.
 2. The rotary steerable system of claim 1, wherein the ratio of the stroke length to the steering section diameter is greater than 0.07.
 3. The rotary steerable system of claim 1, wherein the ratio of the stroke length to the steering section diameter is greater than 0.08.
 4. The rotary steerable system of claim 1, wherein a steering section diameter is at least 5.25 inches, and wherein the stroke length of the piston is between 0.3 inches and 0.5 inches.
 5. The rotary steerable system of claim 4, wherein the stroke length of the piston is about 0.39 inches.
 6. The rotary steerable system of claim 1, wherein a steering section diameter is at least 6.75 inches, and wherein the stroke length of the piston is between 0.4 inches and 0.6 inches.
 7. The rotary steerable system of claim 6, wherein the stroke length of the piston is about 0.54 inches.
 8. The rotary steerable system of claim 1, wherein a steering section diameter is at least 9 inches, and wherein the stroke length of the piston is between 0.6 inches and 0.8 inches.
 9. The rotary steerable system of claim 8, wherein the stroke length of the piston is about 0.71 inches.
 10. The rotary steerable system of claim 1, wherein the steering section includes two piston sets.
 11. The rotary steerable system of claim 1, further comprising a control section.
 12. The rotary steerable system of claim 11, wherein the steering section includes two piston sets.
 13. The rotary steerable system of claim 12, wherein the ratio of the stroke length to the steering section diameter is greater than 0.08.
 14. A rotary steerable system, comprising a steering section, wherein the steering section includes at least one piston, wherein the piston is configured to extend a stroke length radially outward from a default position when activated, wherein a ratio of the stroke length to a steering section diameter is greater than about 0.06, wherein the steering section diameter is a minimum diameter of the steering section, and wherein a ratio of a length of the piston to a diameter of the piston is between 1 and 1.4.
 15. The rotary steerable system of claim 14, wherein the ratio of the length of the piston to the diameter of the piston is between 1.1 and 1.3.
 16. The rotary steerable system of claim 14, wherein the ratio of the length of the piston to the diameter of the piston is about 1.2.
 17. The rotary steerable system of claim 14, wherein the steering section includes two piston sets.
 18. The rotary steerable system of claim 14, further comprising a control section.
 19. The rotary steerable system of claim 18, wherein the steering section includes two piston sets.
 20. The rotary steerable system of claim 19, wherein the ratio of the stroke length to the steering section diameter is greater than 0.08. 